Method of fabricating a remote intelligent communications device

ABSTRACT

A radio frequency intelligent communications device is fabricated from a substrate formed to have conductive lines, at least a portion of which comprise an antenna. An integrated circuit chip and a battery are conductively bonded to the conductive lines on the substrate. A visible spectrum colored liquid resin and a visible spectrum substantially colorless liquid hardener are combined into an epoxy mixture. The liquid hardener has a fluorescent material received therein. Radiation is impinged onto the epoxy mixture effective to cause the fluorescent material to fluoresce. From the fluorescing fluorescent material, degree of homogeneity in the epoxy mixture can be determined. Upon achieving desired homogeneity, the substrate with chip and battery are encapsulated in the epoxy mixture, with the epoxy mixture being cured. The invention also has applicability to epoxy systems and other liquid mixtures having at least to liquid components. The invention also comprises providing first and second liquids where one of said liquids has an invisible component therein. The first and second liquids are combined together into a mixture. The invisible component remains invisible in the mixture upon the combining. After the combining, the component is rendered visible. Degree of homogeneity in the mixture is determined while the component has been rendered visible. After the determining, the component is rendered invisible.

TECHNICAL FIELD

[0001] This invention relates to methods of fabricating radio frequencyremote intelligent communications devices. The invention hasapplicability to methods of processing liquids, epoxy fabricationmethods and processes involving a mixture of different liquids.

BACKGROUND OF THE INVENTION

[0002] Electronic identification systems typically comprise two deviceswhich are configured to communicate with one another. Preferredconfigurations of the electronic identification systems are operable toprovide such communications via a wireless medium.

[0003] One such configuration is described in U.S. patent applicationSer. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee ofthe present application and incorporated herein by reference. Thisapplication discloses the use of a radio frequency (RF) communicationsystem including communication devices. The communication devicesinclude an interrogator and a transponder such as a tag or card.

[0004] The communication system can be used in various identificationand other applications. The interrogator is configured to output apolling signal which may comprise a radio frequency signal including apredefined code. The transponders of such a communication system areoperable to transmit an identification signal responsive to receiving anappropriate command or polling signal. More specifically, theappropriate transponders are configured to recognize the predefinedcode. The transponders receiving the code subsequently output aparticular identification signal which is associated with thetransmitting transponder. Following transmission of the polling signal,the interrogator is configured to receive the identification signalsenabling detection of the presence of corresponding transponders.

[0005] Such communication systems are useable in identificationapplications such as inventory or other object monitoring. For example,a remote identification device is attached to an object of interest.Responsive to receiving the appropriate polling signal, theidentification device is equipped to output an identification signal.Generating the identification signal identifies the presence or locationof the identification device and article or object attached thereto.

SUMMARY

[0006] In but one aspect, the invention comprises a method offabricating a radio frequency intelligent communications device. Asubstrate is formed to have conductive lines, at least a portion ofwhich comprise an antenna. An integrated circuit chip and a battery areconductively bonded to the conductive lines on the substrate. A visiblespectrum colored liquid resin and a visible spectrum substantiallycolorless liquid hardener are combined into an epoxy mixture. The liquidhardener has a fluorescent material received therein. Radiation isimpinged onto the epoxy mixture effective to cause the fluorescentmaterial to fluoresce. From the fluorescing fluorescent material, degreeof homogeneity in the epoxy mixture can be determined. Upon achievingdesired homogeneity, the substrate with chip and battery areencapsulated in the epoxy mixture, with the epoxy mixture being cured.

[0007] The invention also has applicability to epoxy systems and otherliquid mixtures having at least two liquid components. The inventionalso comprises providing first and second liquids where one of saidliquids has an invisible component therein. The first and second liquidsare combined together into a mixture. The invisible component remainsinvisible in the mixture upon the combining. After the combining, thecomponent is rendered visible, for example by exposure to ultravioletradiation. Degree of homogeneity in the mixture is determined while thecomponent has been rendered visible. After the determining, thecomponent is rendered invisible, for example by removing the ultravioletlight source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0009]FIG. 1 is a block diagram of a wireless communication systemincluding an interrogator and a wireless communication device embodyingthe invention.

[0010]FIG. 2 is a front elevational view of the wireless communicationdevice.

[0011]FIG. 3 is a front elevational view of the wireless communicationdevice at an intermediate processing step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0013] This description of the present invention discloses embodimentsof various wireless communication devices. The wireless communicationdevices are fabricated in card configurations (which include tags orstamps) according to some aspects of the present invention. Certainembodiments of invention are methods for producing wirelesscommunication devices such and remote intelligent communication devices(RIC) including radio frequency identification devices (RFID). Theembodiments are illustrative only and other configurations in accordancewith the invention are of course possible, with the invention only beinglimited by the accompanying claims appropriately interpreted inaccordance with the Doctrine Of Equivalents.

[0014] Referring to FIG. 1, a remote intelligent communication device orwireless communication device 10 comprises part of a communicationsystem 12. The remote intelligent communication device is capable offunctions other than the identifying function of a radio frequencyidentification device. A preferred embodiment of the remote intelligentcommunication device includes a processor.

[0015] The communication system 12 includes an interrogator unit 14. Anexemplary interrogator 14 is described in U.S. patent application Ser.No. 08/806,158, filed Feb. 25, 1997, assigned to the assignee of thepresent application and incorporated herein by reference. The wirelesscommunication device 10 communicates via wireless electronic signals,such as radio frequency (RF) signals, with the interrogator unit 14.Radio frequency signals including microwave signals are utilized forcommunications in a preferred embodiment of communication system 12. Thecommunication system 12 includes an antenna 16 coupled to theinterrogator unit 14.

[0016] Referring to FIG. 2, the wireless communication device 10includes an insulative substrate or layer of supportive material 18. Theterm “substrate” as used herein refers to any supporting or supportivestructure, including but not limited to, a supportive single layer ofmaterial or multiple layer constructions. Example materials for thesubstrate 18 comprise polyester, polyethylene or polyimide film having athickness of 3-10 mils (thousandths of an inch).

[0017] Substrate 18 provides a first or lower portion of a housing forthe wireless communication device 10 and defines an outer periphery 21of the device 10. Substrate 18 includes a plurality of peripheral edges17.

[0018] Referring to FIG. 3, at least one ink layer 19 is applied tosubstrate 18 in preferred embodiments of the invention. Ink layer 19enhances the appearance of the device 10 and conceals internalcomponents and circuitry provided therein. A portion of ink layer 19 hasbeen peeled away in FIG. 3 to reveal a portion of an upper surface 25 ofsubstrate 18. In other embodiments, plural ink layers are provided uponupper surface 25.

[0019] A support surface 20 is provided to support components andcircuitry formed in later processing steps upon substrate 18. Inembodiments wherein at least one ink layer 19 is provided, supportsurface 20 comprises an upper surface thereof as shown in FIG. 3.Alternatively, upper surface 25 of substrate 18 operates as the supportsurface if ink is not applied to substrate 18.

[0020] A patterned conductive trace 30 is formed or applied over thesubstrate 18 and atop the support surface 20. Conductive trace 30 isformed upon ink layer 19, if present, or upon substrate 18 if no inklayer is provided. A preferred conductive trace 30 comprises printedthick film (PTF). The printed thick film comprises silver and polyesterdissolved into a solvent. One manner of forming or applying theconductive trace 30 is to screen or stencil print the ink on the supportsurface 20 through conventional screen printing techniques. The printedthick film is preferably heat cured to flash off the solvent and UVcured to react UV materials present in the printed thick film.

[0021] The conductive trace 30 forms desired electrical connections withand between electronic components which will be described below. In oneembodiment, substrate 18 forms a portion of a larger roll of polyesterfilm material used to manufacture multiple devices 10. In such anembodiment, the printing of conductive trace 30 can take placesimultaneously for a number of the to-be-formed wireless communicationdevices.

[0022] The illustrated conductive trace 30 includes conductive lines andpatterns, such as an electrical connection 28, a first connectionterminal 53 (shown in phantom in FIG. 3) and a second connectionterminal 58. Conductive trace 30 additionally defines transmit andreceive antennas 32, 34 in one embodiment of the invention. Antennas 32,34 are suitable for respectively transmitting and receiving wirelesssignals or RF energy. Transmit antenna 32 constitutes a loop antennahaving outer peripheral edges 37. Receive antenna 34 constitutes twoelongated portions individually having horizontal peripheral edges 38 a,which extend in opposing directions, and substantially parallel verticalperipheral edges 38 b.

[0023] Other antenna constructions are of course possible. Inparticular, both transmit and receive operations are implemented with asingle antenna in alternative embodiments of the present invention. Bothantennas 32, 34 preferably extend or lie within the confines ofperipheral edges 17 and outer periphery 21 and define a plane (shown inFIG. 4).

[0024] One embodiment of a wireless communication device 10 includes apower source 52, an integrated circuit chip 54, and capacitor 55. Powersource 52, capacitor 55, and integrated circuit chip 54 are provided andmounted on support surface 20 and supported by substrate 18. Thedepicted power source 52 is disposed within transmit antenna 32 ofwireless communication device 10. Capacitor 55 is electrically coupledwith loop antenna 32 and integrated circuit 54 in the illustratedembodiment.

[0025] Power source 52 provides operational power to the wirelesscommunication device 10 and selected components therein, includingintegrated circuit 54. In the illustrated embodiment, power source 52comprises a battery. In particular, power source 52 is preferably a thinprofile battery which includes first and second terminals of oppositepolarity. More particularly, the battery has a lid or negative (i.e.,ground) terminal or electrode, and a can or positive (i.e., power)terminal or electrode.

[0026] Conductive epoxy is applied over desired areas of support surface20 using conventional printing techniques, such as stencil or screenprinting, to assist in component attachment described just below.Alternately, solder or another conductive material is employed insteadof conductive epoxy. The power source 52 is provided and mounted onsupport surface 20 using the conductive epoxy. Integrated circuit 54 andcapacitor 55 are also provided and mounted or conductively bonded on thesupport surface 20 using the conductive epoxy. Integrated circuit 54 canbe mounted either before or after the power source 52 is mounted on thesupport surface 20.

[0027] Integrated circuit chip 54 includes suitable circuitry forproviding wireless communications. For example, in one embodiment,integrated circuit chip 54 includes a processor 62, memory 63, andwireless communication circuitry or transponder circuitry 64 (components62, 63, 64 are shown in phantom in FIG. 3) for providing wirelesscommunications with interrogator unit 14. An exemplary and preferredintegrated circuit 54 is described in U.S. patent application Ser. No.08/705,043, incorporated by reference above.

[0028] One embodiment of transponder circuitry 64 includes a transmitterand a receiver respectively operable to transmit and receive wirelesselectronic signals. In particular, transponder circuitry 64 is operableto transmit an identification signal responsive to receiving a pollingsignal from interrogator 14. In the described embodiment, processor 62is configured to process the received polling signal to detect apredefined code within the polling signal. Responsive to the detectionof an appropriate polling signal, processor 62 instructs transpondercircuitry 64 to output an identification signal. The identificationsignal contains an appropriate code to identify the particular device 10transmitting the identification signal in certain embodiments. Theidentification and polling signals are respectively transmitted andreceived via antennas 32, 34 of the device 10.

[0029] First and second connection terminals 53, 58 are coupled to theintegrated circuit 54 by conductive epoxy in accordance with a preferredembodiment of the invention. The conductive epoxy also electricallyconnects the first terminal of the power source 52 to the firstconnection terminal 53. In the illustrated embodiment, power source 52is placed lid down such that the conductive epoxy makes electricalcontact between the negative terminal of the power source 52 and thefirst connection terminal 53.

[0030] Power source 52 has a perimetral edge 56, defining the secondpower source terminal, which is provided adjacent second connectionterminal 58. In the illustrated embodiment, perimetral edge 56 of thepower source 52 is cylindrical, and the connection terminal 58 isarcuate and has a radius slightly greater than the radius of the powersource 52, so that connection terminal 58 is closely spaced apart fromthe edge 56 of power source 52.

[0031] Subsequently, conductive epoxy is dispensed relative toperimetral edge 56 and electrically connects perimetral edge 56 withconnection terminal 58. In the illustrated embodiment, perimetral edge56 defines the can of the power source 52. The conductive epoxy connectsthe positive terminal of the power source 52 to connection terminal 58.The conductive epoxy is then cured. Thus, the integrated circuit andbattery are conductively bonded relative to the substrate and to theconductive lines of trace 30.

[0032] An encapsulant, such as encapsulating epoxy material, issubsequently formed following component attachment. In one embodiment,the encapsulant is provided over the entire support surface 20. Suchencapsulates or envelopes the antennas 32, 34, integrated circuit 54,power source 52, conductive circuitry 30, capacitor 55, and at least aportion of the support surface 20 of substrate 18. Such operates toinsulate and protect the components (i.e., antennas 32, 34, integratedcircuit 54, power source 52, conductive circuitry 30 and capacitor 55).

[0033] An exemplary encapsulant is a flowable encapsulant. The flowableencapsulant is applied over substrate 18 and subsequently curedfollowing the appropriate covering of the desired components. In thepreferred embodiment, such encapsulant constitutes a two-part epoxyperhaps including fillers such as silicon and calcium carbonate. Thepreferred two-part epoxy is sufficient to provide a desired degree offlexible rigidity. Such encapsulation of wireless communication device10 is described in U.S. patent application Ser. No. 08/800,037, filedFeb. 13, 1997, assigned to the assignee of the present application, andincorporated herein by reference. Other encapsulant materials ofinsulative layer 60 can be used in accordance with the presentinvention. Encapsulation would preferably occur from fabrication ofmultiple device patterns 10 formed on a single substrate sheet, and thencutting individual devices 10 from the sheet after encapsulation andcure.

[0034] Fabrication of the epoxy encapsulant material presents somechallenges. Specifically, the preferred epoxy comprises a two-componentsystem having a liquid resin material and a liquid hardener material. Apresently preferred resultant color for the cured encapsulant is lightgrey. The resin typically constitutes three times the volume of thehardener within the liquid mixture from which the two-part system cures.In the preferred embodiment, the liquid resin is fabricated to be greyin color in light within the visible electromagnetic radiation spectrum.The hardener is clear or colorless in light within the visible spectrum.It is highly desirable that adequate and complete mixing of theresin/hardener two-component epoxy system occur prior to dispensing orotherwise providing the liquid encapsulant atop the substrate, chip, andbattery. This is difficult to discern visually where one of the liquidmixing components is clear and the other is not.

[0035] A color-changing phenomenon might be utilized, but may alsoadversely affect the desired finished color of the product. For example,consider provision of a yellowish-colored hardener and a bluish-coloredresin. The combination of these two natural colors produces green.Complete homogeneity in the mix of two such components could bedetermined quite easily visually by verifying uniform green coloringthroughout the mix. However where the desired finished product is to besome color other than green, an obviously less than desirable resultoccurs.

[0036] In accordance with one aspect of the invention, at least one ofthe liquid resin and the liquid hardener is provided to have afluorescent material therein. An example would be any of the T-700Series, T-1020 Series, T-100-OS Series aqueous or oil solublefluorescent tracers available from Shannon Luminous Materials, Inc., ofSanta Ana, Calif. Such materials are understood to have been utilized inthe prior art as additives to liquid coatings to assure complete coatingof a substrate covered by the coating. Preferably, the other of theliquid resin or liquid hardener is provided to have no fluorescentmaterial therein, or less preferably have some other distinguishingfluorescent material therein.

[0037] The liquid resin and the liquid hardener are then combined intoan epoxy mixture, and ideally stirred to achieve desired completemixing. Thereafter or during mixing, radiation of suitable wave lengthis impinged onto the epoxy mixture effective to cause the fluorescentmaterial to fluoresce. From the fluorescing fluorescent material, degreeof homogeneity in the epoxy mixture can be determined. Suchdetermination could occur simply by the human eye, or by more automatedspectrographic means. For example, where the fluorescing material wasfluorescent in ultraviolet light, ultraviolet radiation could beimpinged upon the mixture with the results being viewed by a human eye.If the mixture glowed uniformly throughout, complete mixing has occurredsuch that the mixture is substantially homogenous. If on the other handthe mixture has specs or streaks of fluorescence and lack offluorescence or uniform fluorescence, such would evidence that completemixing has not yet occurred. Such can also be used to determine if thehardener has even been added to the mixture.

[0038] In the preferred embodiment, the fluorescent material ispreferably placed within the hardener, which is also the lower volumecomponent of the mixture and also in this embodiment a component whichis colorless in light within the visible spectrum or substantiallyclear. Also preferably, the liquid resin is provided to be substantiallyvoid of any fluorescent material. Ideally, the epoxy mixture hassubstantially the same color and light within the visible spectrum aswould exist if the fluorescent material, when not fluorescing, were notpresent in the epoxy mixture.

[0039] Once desired homogeneity was achieved as evidenced by examinationof the fluorescent material, the substrate with chip and battery wouldbe encapsulated within the epoxy mixture. After such encapsulating, theepoxy mixture would then essentially cure into a solidified mass.

[0040] Although specifically motivated for epoxy fabrication methods,and for use of such methods in remote intelligent communication devices,the invention is believed to have applicability in other methods ofprocessing liquid mixtures comprising at least two different liquids.For example, the invention is seen to have applicability for any twomixture combinations of two liquids whereby a fluorescent material isprovided into at least one of the liquids prior to combination with asecond liquid to form a mixture. Degree of homogeneity in the mixturecan be determined qualitatively or quantitatively by causing thefluorescent material to fluoresce and analyzing its presence throughoutthe mixture. Preferably, where the volume of liquids within the mixtureis different, the fluorescent material is provided in the lower volumecomponent.

[0041] Liquid mixture systems involving three or more different liquidscould of course also be utilized in combination with a fluorescentmaterial in preferably only one of the liquids to determine a degree ofhomogeneity in a resultant mixture of such liquids.

[0042] In accordance with the above-described preferred embodiments, thefluorescent material ideally comprises an invisible component which isprovided in at least one of the first and second liquids. Such componentideally remains invisible in a mixture of the liquids. After forming themixture, the invisible component in the mixture is rendered visible, inthe above example by impinging ultraviolet radiation, and the degree ofhomogeneity in the mixture is determined therefrom. After suchdetermination, and if desired further mixing, the invisible component isreturned to its invisible state, in the above example, by removing theimpinging radiation source. Thus, resultant color in the finished andsolidified product is not impacted by the component from whichhomogeneity is determined.

[0043] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of processing at least two liquids comprising: providing afirst liquid having a fluorescent material therein; providing a secondliquid; combining the first and second liquids together into a mixture;impinging radiation onto the mixture effective to cause the fluorescentmaterial to fluoresce; and from the fluorescing fluorescent material,determining degree of homogeneity in the mixture.
 2. The method of claim1 wherein the fluorescent material is colorless in light within thevisible spectrum when not fluorescing.
 3. The method of claim 1 whereinthe first liquid has color in light within the visible spectrum.
 4. Themethod of claim 1 wherein the second liquid is colorless in light withinthe visible spectrum.
 5. The method of claim 1 wherein the first liquidhas color in light within the visible spectrum, and the second liquid iscolorless in light within the visible spectrum.
 6. The method of claim 1comprising a third liquid in the mixture.
 7. The method of claim 1wherein the second liquid is substantially void of any fluorescentmaterial.
 8. The method of claim 1 wherein the mixture is substantiallyvoid of any fluorescent material other than that provided from the firstliquid.
 9. The method of claim 1 wherein the first and second liquidshave different volumes within the mixture, the first liquid being oflesser volume than the second liquid.
 10. The method of claim 1 whereinthe first and second liquids have different volumes within the mixture,the first liquid being of greater volume than the second liquid.
 11. Anepoxy fabrication method comprising: providing a liquid resin and aliquid hardener, at least one of the liquid resin and the liquidhardener having a fluorescent material therein; combining the liquidresin and the liquid hardener into an epoxy mixture; impinging radiationonto the epoxy mixture effective to cause the fluorescent material tofluoresce; and from the fluorescing fluorescent material, determiningdegree of homogeneity in the epoxy mixture.
 12. The method of claim 11wherein the fluorescent material is provided in the hardener.
 13. Themethod of claim 11 wherein the fluorescent material is provided in theresin.
 14. The method of claim 11 wherein the fluorescent material isprovided in the hardener, and the resin has a greater volume in theepoxy mixture than does the hardener.
 15. The method of claim 11 whereinthe epoxy mixture is substantially void of any liquid material otherthan the hardener and the resin.
 16. The method of claim 11 wherein theresin has color in light within the visible spectrum.
 17. The method ofclaim 11 wherein the hardener is colorless in light within the visiblespectrum.
 18. The method of claim 11 wherein the resin has color inlight within the visible spectrum, and the hardener is colorless inlight within the visible spectrum.
 19. An epoxy fabrication methodcomprising: providing a liquid resin and a liquid hardener, the liquidhardener having a fluorescent material therein and the liquid resinbeing substantially void of any fluorescent material; combining theliquid resin and the liquid hardener into an epoxy mixture having agreater volume of resin than hardener, the epoxy mixture havingsubstantially the same color in light within the visible spectrum aswould exist if the fluorescent material when not fluorescing were notpresent in the epoxy mixture; impinging radiation onto the epoxy mixtureeffective to cause the fluorescent material to fluoresce; and from thefluorescing fluorescent material, determining degree of homogeneity inthe epoxy mixture.
 20. The method of claim 19 wherein the epoxy mixtureis substantially void of any liquid material other than the hardener andthe resin.
 21. The method of claim 19 wherein the resin has color inlight within the visible spectrum.
 22. The method of claim 19 whereinthe hardener is colorless in light within the visible spectrum.
 23. Themethod of claim 19 wherein the resin has color in light within thevisible spectrum, and the hardener is colorless in light within thevisible spectrum.
 24. A method of fabricating a remote intelligentcommunications device comprising: providing a substrate havingconductive lines formed thereon, the conductive lines comprising anantenna; conductively bonding an integrated circuit chip and a batteryto the conductive lines on the substrate; providing a visible spectrumcolored liquid resin and a visible spectrum substantially colorlessliquid hardener, the liquid hardener having a fluorescent materialtherein; combining the liquid resin and the liquid hardener into anepoxy mixture having a volumetric ratio of resin to hardener of at leastabout 2; impinging radiation onto the epoxy mixture effective to causethe fluorescent material to fluoresce; from the fluorescing fluorescentmaterial, determining degree of homogeneity in the epoxy mixture; uponachieving desired homogeneity, encapsulating the substrate with chip andbattery in the epoxy mixture; and after encapsulating, curing the epoxymixture.
 25. The method of claim 19 wherein the epoxy mixture issubstantially void of any liquid material other than the hardener andthe resin.
 26. A method of processing at least two liquids comprising:providing first and second liquids, one of the first and second liquidscomprising a component which is invisible; combining the first andsecond liquids together into a mixture, the component remaininginvisible in the mixture upon the combining; after the combining,rendering the component visible; determining degree of homogeneity inthe mixture while the component has been rendered visible; and after thedetermining, rendering the component invisible.
 27. The method of claim26 further comprising curing the mixture into a solid mass after thedetermining.
 28. The method of claim 26 wherein the one of the first andsecond liquids is colorless in light within the visible spectrum. 29.The method of claim 26 wherein the other of the first and second liquidshas color in light within the visible spectrum.
 30. The method of claim26 wherein the one of the first and second liquids is colorless in lightwithin the visible spectrum, and the other of the first and secondliquids has color in light within the visible spectrum.
 31. The methodof claim 26 wherein the one of the first and second liquids has a lesservolume within the mixture than the other of the first and secondliquids.
 32. A method involving a mixture of different liquidscomprising: rendering an invisible component in the mixture visible anddetermining therefrom degree of homogeneity of the mixture; andreturning the invisible component to its invisible state.
 33. The methodof claim 32 further comprising solidifying the mixture into a solidmass.
 34. The method of claim 32 further comprising solidifying themixture into a solid mass after the returning.
 35. The method of claim32 wherein at least one of the liquids in the mixture is colorless inlight within the visible spectrum.
 36. The method of claim 32 whereinthe mixture has color in light within the visible spectrum.